Titanium phenoxides

Crocker and co-workers reported the use of 108 as starting material in the preparation of monomeric titanasilsesquioxane phenoxide derivatives. Heating of the isopropoxide precursor with phenols resulted in elimination of i-PrOH and formation of the corresponding titanium phenoxide complexes (Scheme 36). 

The hydroxyalkylation of phenols with chiral glyoxylates, followed by hydrolysis, gives regioselectively 2-hydroxymandelic acids with high enantioselectivity (eqnation 28). The crystal-structure determination of the titanium phenoxide complex shows evidence for chelation-controlled reaction giving the observed high enantioselectivities . ... 

Trost and coworkers developed a chiral zinc phenoxide for the asymmetric aldol reaction of acetophenone or hydroxyacetophenone with aldehydes (equations 62 and 63) . This method does not involve the prior activation of the carbonyls to silyl enol ethers as in the Mukaiyama aldol reactions. Shibasaki and coworkers employed titanium phenoxide derived from a phenoxy sugar for the asymmetric cyanosilylation of ketones (equation 64). 2-Hydroxy-2 -amino-l,l -binaphthyl was employed in the asymmetric carbonyl addition of diethylzinc , and a 2 -mercapto derivative in the asymmetric reduction of ketones and carbonyl allylation using allyltin ° . ... 

The preparation of Tbf titanium phenoxides involved the development of a suitable type of chlorotitanium aryloxides as starting material since most complexes of the general formula ClTi(OAr)3Xn (Ar = any phenyl, X = Lewis... 

Dialkylaminoethyl acryhc esters are readily prepared by transesterification of the corresponding dialkylaminoethanol (102,103). Catalysts include strong acids and tetraalkyl titanates for higher alkyl esters and titanates, sodium phenoxides, magnesium alkoxides, and dialkyitin oxides, as well as titanium and zirconium chelates, for the preparation of functional esters. Because of loss of catalyst activity during the reaction, incremental or continuous additions may be required to maintain an adequate reaction rate. 

Long-chain esters of pentaerythritol have been prepared by a variety of methods. The tetranonanoate is made by treatment of methyl nonanoate [7289-51-2] and pentaerythritol at elevated temperatures using sodium phenoxide alone, or titanium tetrapropoxide in xylene (12). PhenoHc esters having good antioxidant activity have been synthesized by reaction of phenols or long-chain aUphatic acids and pentaerythritol or trimethyl olpropane (13). 

Certain half-sandwich phenoxides have been shown to be highly active olefin polymerization catalysts. For example, the zirconium complex (60) polymerizes ethylene with an activity of 1,220 gmmol-1 h-1 bar-1.181 A similar titanium complex (61) displays an activity of 560gmmol ll bar 1 at 60°C.182-189 Comparable activities were also recorded for the copolymerization of ethylene with 1-butene and 1-hexene. 

The addition of a base, typically ammonia, to mixtures of transition metal halides and alcohols allows the synthesis of homoleptic alkoxides and phenoxides for a wide range of metals. Anhydrous ammonia was first used in the preparation of titanium alkoxides where the reaction is forced to completion by the precipitation of ammonium chloride.41 Although useful for the synthesis of simple alkoxides and phenoxides of Si, Ge, Ti, Zr, Hf, V, Nb, Ta and Fe, as well as a number of lanthanides,42-47 the method fails to produce pure /-butoxides of a number of metals.58 Presumably, secondary reactions between HC1 and Bu OH take place. However, mixing MC14(M = Ti, Zr) with the Bu OH in the presence of pyridine followed by addition of ammonia proves successful, giving excellent yields of the M(OBul)4 complexes.59... 

A mixture of phenol and aluminum sulfide is rapidly converted to the phenoxide on heating with the evolution of H2S.20 Similarly, titanium and silicon phenoxides can be prepared directly from their sulfides (equation 38).119,120... 

The alcoholysis of other derivatives than alkoxides themselves (method 4) has not found any broad application in the case of titanium derivatives however, the use of Ti(NMe2)4 for this purpose has been reported [1579], Phenoxides... 

A compound similar to (XIII) has also been prepared from the pyrocatechol compound Ti(02C6H4)Cl2 by reduction with sodium amalgam in THF, and has been formulated to be similar to (XIII) with the two phenoxide groups at each titanium being replaced by the pyrocatecholate dianion. The ESR signal from both these complexes suggests the presence of one unpaired electron per dimer (50). 

Titanium tetra-2-naphthyl- oxide Titanium tetra- re s o rcinylo xi de Titanium tetra- s te arylo xide Titanium tetra-2,4,6-trinitro -phenoxide [36452-22-9] [3407540-6] [84215-67-8] Ti(OC10H7)4 Ti(02C(.H4)2 Ti(OCi8H37)4 Ti(0C6H2(N02)3)4 60-64 c... 

Scheme 350 shows the structures of a number of mono-Cp titanium complexes with more elaborately substituted aryloxo ligands. The compounds are formed by the reaction of Cp TiCl3 with 1 equiv. of the substituted phenol in the presence of an excess of pyridine or by treatment of the lithium phenoxide with Cp TiCl3 some of them have been... 

Although strictly outside the reactions of prenyiphenolic compounds the extensive work on the regiospecific general synthesis of chrom-3-enes (2H-benzo[b]pyrans), in particular2,2-dimethylchromenes, from the reaction of metal phenoxides with 3-methylbut-3-enal is very noteworthy. In the general procedure a solution of titanium tetraethoxide (0.025 mol) in toluene was treated with the phenol (0.1 mol) in toluene and the ethanol formed removed by distillation over... 

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